Synergy of Mn and Ni enhanced catalytic performance for toluene combustion over Ni-doped α-MnO2 catalysts

A series of metal-doped α-MnO2 catalysts (M-MnO2, M = Ni, Cu, Co) were synthesized via a novel ethylene glycol (EG) reduction strategy for the first time, based on initial reduction of KMnO4 with EG and subsequent heteroatom doping at room temperature, and used for catalytic toluene combustion. The obtained catalysts have been full characterized by XRD, XRF, N2 adsorption, SEM, TEM, XPS, H2-TPR, O2-TPD, and C7H8-TPSR. It was found that the catalytic properties of α-MnO2 can be significantly improved by nickel doping, a remarkable low-temperature performance (T90 = 199 °C) has been achieved over Ni-MnO2 catalyst, which is among the best reported values. Meanwhile, Ni-MnO2 has also exhibited high catalytic stability with strong water tolerance (5 vol%) in the oxidation of toluene. Herein, the relationship between catalyst structure and catalytic activity has been elucidated. The outstanding catalytic properties can be related to the synergistic effect between Mn and doped Ni species for the adsorption and activation of toluene. Significantly, the substitutional doping of Ni2+ into octahedra MnO6 frameworks could not only improve the redox properties, lattice oxygen mobility and the formation of more active lattice oxygen, but also promote the toluene adsorption. Additionally, a potential catalytic reaction process base on the Mars and van Krevelen mechanism was also proposed. Hence, this work paves a new way for the design and synthesis of high efficient catalysts for the elimination of volatile organic compounds.